1. Field of the Invention
The present invention relates to a recording medium and a manufacturing method thereof, and an inkjet recording method using the same.
2. Description of the Related Art
Inkjet recording apparatuses have simple structures, and inkjet recording performed by use of such inkjet recording apparatuses allows high-quality image recording. Inks used in inkjet recording are prepared so as to have viscosity in the region of several mPa·s to 30 mPa·s and designed to have surface tension in the region of 20 mN/m to 40 mN/m so that they can be discharged from inkjet heads.
In order to adjust the viscosity of an ink to fall within the above range, an ink solvent in a proportion of 50 to 90% by mass is generally mixed in each ink. Water, an organic solvent, an oil, a photopolymerizable monomer or the like can be used as the ink solvent and, in particular, water is widely used due to the comparative environmental friendliness thereof. Further, in order to avoid clogging in the discharge nozzles of an inkjet head due to drying of an ink solvent, a high boiling point solvent, such as glycerin, is generally used as an ink solvent.
However, when a large amount of ink solvent is present in a recording medium on which images are portrayed with inks, the large amount of ink solvent tends to cause image bleeding and mixing between colors. Therefore, inkjet-specific paper having a solvent absorbing layer (an ink accepting layer) provided thereon with a thickness of about 20 to 30 μm (see FIG. 5) is used as a recording medium, whereby image bleeding and mixing between colors are prevented from occurring.
In the case of water-based inks using water as an ink solvent, paper deformation such as curling occurs due to permeation of water into base paper during recording. However, as shown in FIG. 5, when the recording medium 200 has a solvent absorbing layer 22 on a base paper 21, permeation of water into the base paper can be prevented and paper deformation can be avoided.
When attempts are made to form a graphical image having a high image density and a high image-area rate, the amount of ink per unit area on a recording medium becomes large, and it becomes impossible for the solvent absorption layer to inhibit permeation of the ink solvent into the base paper. Therefore, waterproof paper covered with a resin layer, such as a polyolefin layer, (e.g., laminated paper) is generally used (see, for example, JP-A Nos. 2005-238829 and 2005-96285).
In recent years, in addition to the sectors of office printers, home printers and the like, inkjet technology has been increasingly applied to the field of commercial printing. In the field of commercial printing, prints having photograph-like surfaces that completely prevent permeation of an ink solvent into base paper are not required and, rather, a print texture such as that of printing paper for general purpose use is required. For this reason, when the solvent absorbing layer included in a recording medium has a comparatively large thickness of 20 to 30 μm, there arise limitations on, for example, the surface gloss, texture and stiffness (sturdiness) of the recording medium. Thus, application of inkjet technology in the field of commercial printing is limited to posters, ledger sheet printing and the like in which the limitations on, for example, surface gloss, texture and stiffness (sturdiness) of the recording media are less stringent.
In addition, production of the recording medium entails high costs due to the necessity of including a solvent absorbing layer and a waterproof layer, which also contribute to the above limitations.
In recent years, in particular, speeding-up of printing has been sought after, and in inkjet recording performed by use of a high-speed printing system such as a single-path system, there has been a problem whereby even the inkjet recording-specific paper discussed above cannot sufficiently absorb an ink solvent, which results in intercolor bleeding.
As a means for solving this problem, a printing method in which droplets of a liquid composition containing an acid having a function of aggregating ink are applied to a recording medium before ink droplets are applied to the recording medium has been disclosed (see, for example, JP-A No. 2004-10633). Further, a method of improving the pigment ink suitability by making a pH adjustment on the surface of an ink receiving layer has been disclosed (see, for example, JP-A No. 2007-130791).
However, none of the printing methods or the recording media disclosed in the patent documents cited above ensure water resistance enhanced to the extent that paper is prevented from deforming due to curling or the like when, for example, a large amount of ink solvent is applied thereto.
The printing method disclosed in JP-A No. 2004-10633 complicates the printing process, and not only poses an impediment to speeding-up of the process but is also problematic in terms of cost. Accordingly, it is difficult to view this method as an appropriate plan for improvements. In addition, the aggregation effect of the pigment is so strong that it results in occurrence of print failures such as a bronzing phenomenon in which areas printed in black color appear to be discolored to brown immediately after printing.
The recording medium as disclosed in JP-A No. 2007-130791 has a high P/B ratio (particles/binder ratio) in the blocking layer provided between the base paper and the ink receiving layer and, therefore, the solvent in the ink permeates into the base paper at the time of inkjet recording and causes a curling problem whereby paper deformation extends over the entire paper and a cockling problem whereby unevenness develops in parts of the paper. In particular, when forming graphical images having high image density and a high image-area rate, the amount of ink per unit area on a recording medium becomes large and the foregoing problems are further aggravated.
As discussed above, conventionally-known techniques are unable to provide inkjet recording media that can prevent image failure such as intercolor bleeding, bleeding over time and bronzing when the inkjet recording media undergo high-speed printing, and that have excellent anti-curling property.